Smarter search radius formula for map matching

Author: kerrick-lyft

include/engine/api/match_parameters.hpp

@@ -28,6 +28,13 @@ SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #ifndef ENGINE_API_MATCH_PARAMETERS_HPP
 #define ENGINE_API_MATCH_PARAMETERS_HPP
 
+#define SEARCH_RADIUS_BASE_DEFAULT 45
+#define SEARCH_RADIUS_BASE_LIMIT 100
+#define SEARCH_RADIUS_MULTIPLIER_DEFAULT 3.5
+#define SEARCH_RADIUS_MULTIPLIER_LIMIT 10
+#define SEARCH_RADIUS_MAX_DEFAULT 200
+#define SEARCH_RADIUS_MAX_LIMIT 500
+
 #include "engine/api/route_parameters.hpp"
 
 #include <vector>
@@ -67,10 +74,20 @@ struct MatchParameters : public RouteParameters
     }
 
     std::vector<unsigned> timestamps;
+
+    double search_radius_base = SEARCH_RADIUS_BASE_DEFAULT;
+    double search_radius_multiplier = SEARCH_RADIUS_MULTIPLIER_DEFAULT;
+    double search_radius_max = SEARCH_RADIUS_MAX_DEFAULT;
+
     bool IsValid() const
     {
         return RouteParameters::IsValid() &&
-               (timestamps.empty() || timestamps.size() == coordinates.size());
+               (timestamps.empty() || timestamps.size() == coordinates.size()) &&
+               search_radius_base >= 0 && search_radius_multiplier >= 0 && search_radius_max > 0 &&
+               // limit the search_radius parameters to sane values to prevent overloading the server
+               search_radius_base <= SEARCH_RADIUS_BASE_LIMIT &&
+               search_radius_multiplier <= SEARCH_RADIUS_MULTIPLIER_LIMIT &&
+               search_radius_max <= SEARCH_RADIUS_MAX_LIMIT;
     }
 };
 }

include/server/api/match_parameter_grammar.hpp

@@ -33,13 +33,33 @@ struct MatchParametersGrammar final : public RouteParametersGrammar<Iterator, Si
             (qi::uint_ %
              ';')[ph::bind(&engine::api::MatchParameters::timestamps, qi::_r1) = qi::_1];
 
+        search_radius_base_rule =
+            qi::lit("search_radius_base=") > qi::double_[
+                ph::bind(&engine::api::MatchParameters::search_radius_base, qi::_r1) = qi::_1];
+
+        search_radius_multiplier_rule =
+            qi::lit("search_radius_multiplier=") > qi::double_[
+                ph::bind(&engine::api::MatchParameters::search_radius_multiplier, qi::_r1) = qi::_1];
+
+        search_radius_max_rule =
+            qi::lit("search_radius_max=") > qi::double_[
+                ph::bind(&engine::api::MatchParameters::search_radius_max, qi::_r1) = qi::_1];
+
         root_rule = BaseGrammar::query_rule(qi::_r1) > -qi::lit(".json") >
-                    -('?' > (timestamps_rule(qi::_r1) | BaseGrammar::base_rule(qi::_r1)) % '&');
+                    -('?' > (timestamps_rule(qi::_r1) |
+                             search_radius_base_rule(qi::_r1) |
+                             search_radius_multiplier_rule(qi::_r1) |
+                             search_radius_max_rule(qi::_r1) |
+                             BaseGrammar::base_rule(qi::_r1))
+                            % '&');
     }
 
   private:
     qi::rule<Iterator, Signature> root_rule;
     qi::rule<Iterator, Signature> timestamps_rule;
+    qi::rule<Iterator, Signature> search_radius_base_rule;
+    qi::rule<Iterator, Signature> search_radius_multiplier_rule;
+    qi::rule<Iterator, Signature> search_radius_max_rule;
 };
 }
 }

src/engine/plugins/match.cpp

@@ -139,15 +139,11 @@ Status MatchPlugin::HandleRequest(const std::shared_ptr<datafacade::BaseDataFaca
                        parameters.radiuses.end(),
                        search_radiuses.begin(),
                        [](const boost::optional<double> &maybe_radius) {
-                           if (maybe_radius)
-                           {
-                               return *maybe_radius * RADIUS_MULTIPLIER;
-                           }
-                           else
-                           {
-                               return DEFAULT_GPS_PRECISION * RADIUS_MULTIPLIER;
-                           }
+                           double in_radius = maybe_radius ? *maybe_radius : DEFAULT_GPS_PRECISION;
 
+                           return std::min(
+                               in_radius * parameters.search_radius_multiplier + parameters.search_radius_base,
+                               parameters.search_radius_max);
                        });
     }